Actual experiences mod'ing laptop bricks?

[dp]

...
I can also imagine a power supply telling the laptop how much power
it is *actually* using (adding those monitoring components *outside*
the physical constraints of the laptop itself) so the laptop can
better calibrate its battery monitoring algorithms (instead of
just watching Vbat without any real idea as to how quickly it
*should* be falling -- when operating on battery).

Hi Don,
of course we can imagine lots of things but moving the charger
control part outside of the laptop would likely be impractical.
For the time being, that is . Wait until they get as thin as
a sheet of paper....

It does not take much, here is most of the charger circuitry
of a one-off thingie I did for a university lab not so long ago:
http://tgi-sci.com/misc/swgps3.gif . Not that much one can save
in terms of space - and I have been conservative (e.g. put a 3.3V
zener and don't think how ADC inputs on the MCU react to clamping
currents into on a neighbour input). (here is the whole
thing: http://tgi-sci.com/dsv/swg800.gif ,
http://tgi-sci.com/misc/PICT6999.avi , http://tgi-sci.com/dsv/swgboard.gif ).

OTOH I know what a pain it can be to connect to a power adapter you
have not tested. I went to lengths I still can't believe myself
on the netmca to protect against various power input events (it has
no battery to buffer things somewhat, the input feeds the convertors
directly). Things were even more complicated given that the processor
(an MPC5200B) needed certain rise times on its 1.5V power so its
PLL feedback amp would not go into saturation before the oscillator
would get to work OK.... In hindsight if I had made the power adaptor
identifiable and somehow simply not starting the whole thing unless
the ID has been seen things might have been easier (not so sure but it
could have been an alternative path).
Having a battery makes things easier to control but with li-ion things
also can get hazardous so it might be not such a bad idea to have the
charger identify itself, at least from a legal point of view.

Dimiter

 

[Chris Jones]

Hi,

I've got a ~200W laptop brick on which I'd like to tweek the
output voltage (~5% -- 19.5V down to 18.5V). Anyone know what
sort of margins they design into these? I'm not keen on risking
the laptop for the sake of a $10 power supply... (i.e., "it
*should* work" is not an acceptable reply :> )

Thx,
--don

Why not get a couple of power Schottky diodes and put them in series
with the DC output, to drop the voltage a bit. You can get the diodes
out of an old ATX power supply from a dumpster. The diodes could be
bolted to a 1 inch wide piece of aluminium strip as heatsink and spliced
inline with the DC cable and covered with heatshrink. It would be
somewhat wasteful and would get a bit warm if the laptop ever really
draws 200W, but it would avoid cracking open the plastic case of the
charger and reverse engineering it. Also there is very little risk of
the diodes not behaving as one would expect them to, at least within
their ratings.

Chris